Breech locking mechanism



Sept. 15, 1953 c. E. slMPsoN BREECH LOCKING MECHANISM Filed Sept. 22, 1949 2 Sheets-Sheet l Nh SJ.

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gmac/nto@ lnrenneE-m]nam1-L Sept. 15, 1953 c. E. slMPsoN 2,651,974

BREECH LOCKING MECHANISM Filed septjzz. 1949 2 Sheets-Sheet 2 Blurent@ E .En'mPam-L Patented Sept. l5, 1953 UNITED S TAT E to the United States of America as represented by the Secretary of War Application September 22, 1949, Serial No. 117,101

(Granted under Title 35, U. S.`Code (1952),

sec. 266) 8 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to breech lockingA means for firearms and particularly to an improved breech lock mechanism of the type wherein the locking members are provided with an' exterior roll surface and functionl at right angles to' the longitudinal axis of the breech member.

@ne example of the above type of breech locking mechanism comprises a pair of cylindrical lock members movably retained in a suitable transverse hole formed through the body portion of the bolt. When the latter member enters its closed or battery position, each of such lock members is arranged to be forced sumeiently out of the transverse hole to engage in a suitable arcuate cut provided in some fixed member of the firearm. In order to assure a positive cammin'g action on the lock members for unlocking the boltupon recoil, the radius of cach locking cut is necessarily formed so as to be greater than the radius of the locking portion of the cylindrical lock member. In addition, suflicient clearance is maintained between the sides of the bolt and the iixed member to provide a depth of engagement between the lockingmembers and the respective arcuate locking cuts ofV somewhat less than the radius ofthe locking members. Consequently, when the bolt recoils, sufficient angular thrust is provided between the locking and fixed members tof quickly and positively initiate the camming' actionrequired to unlock thebolt.

However, the aforementioned combination of conditions introduces certain objectionable features which the present invention is designed to eliminate or overcome. vOne such undesirable feature in the locking means of the prior art is the diiculty of maintaining the proper clearance, commonly termed head space, between the breech end of the barrel and the face of the bolt when the latter is in its battery position.v Due to the difference in size between the radius of a locking member and that of the locking out in which it is engaged, it can readily be seen that any change in the depth of engagement therebetween will result in a relatively greater change in the location of the point' of contact between the two surfaces as measured along a line parallel to the longitudinal axis of the bolt. Variation in the location of this point of contact will, of course, permit corresponding longitudinal movement of the bolt despite the engagement -of" thelocking members in the arcuate cuts of the xed member.

Itis therefore apparent that any wear induced in the locking surfaces or any accumulation of tolerances will affect the critical head space relationshipoi the bolt and barrel.

Accordingly, it is an object of this invention to provide in a firearm a simple, reliable, roll-type breech locking mechanism wherein ordinary wear of the moving parts or any normalaccumulation of manufacturing. tolerances will not seriously affect head space.

In the aforementioned prior art type of breech locking mechanism, the locking members are carried in the head of the bolt thereby requiring that a transverse hole be provided therethrough, or alternately, that a pair of axially aligned recesses be formed, one on eitherside oi the bolt, of sufiicient depth to permit full retraction of the roller members therein for unlocking of the bolt. In either event, a substantial amount ci metal must be removed from the body of the bolt thereby requiring a relatively thick body portion in order t0 avoidv the possibility of excessively weakening the structure thereof at the area of the hole or holes. Obviously, it is highly desirable that the recoil'- ing parts of a: high speed firearm be of optimum strength and yet be as light in weight as possible. Furthermore, the necessity of machining suitable arcuate locking cuts'internally in the fixed member of the firearm introduces a complexity of manufacture leading to` a corresponding increase in the cost of production.

it is'therefore a further object of this invention to provide a breech locking mechanism wherein the locking members are carried, when in the unlocked condition, in a xed member of the rirearm thereby permitting a simple, compact and inexpensive construction.

Another detrimental feature in a breech lockn ing mechanism having a full cylindrical locking member protruding from a transverse hole formed in the bolt is the tangential Contact which rexistsbetween the surface of the locking member and the rim of the transverse hole. The strong recoil thrust oi the bolt substantially increases the possibility of deformation of the cylindrical surface oi the roller member at such tangential point ofcontact.

A particular object of this invention, therefore, is the provision of a semi-cylindrical roll-type locking member for a breech locking mechanism which' will not beV subject to excessive deformation during the pressure period which exists prior to the actual unlocking movement.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a top elevational view of the breech locking mechanism of this invention, drawn partly in cross-section and showing the recoiling parts in the unlocked position of the bolt.

Fig. 2 is a view similar to Fig. 1 but showing the recoiling parts in the battery position with the bolt locked.

Fig. 3 is a fragmentary cross-sectional view taken along the line 3-3 in Fig. 5 showing the manner in which the locking members engage the bolt.

Fig. 4 is a cross-sectional view taken along the line 4-4 in Fig. 5.

Fig. 5 is a side elevational view of that portion of a firearm which contains the breech locking mechanism of this invention.

Fig. 6 is an exploded view showing in isometric the novel parts of the breech locking mechanism.

Fig. 7 is a top view of the locking members showing their position relative to the barrel locking sleeve in the locked and unlocked position.

Fig. 8 is a rear end view of the breech lock actuator.

Fig. 9 is a side elevational view of the bolt assembly shown partly in cross-section.

Fig. 10 is a view similar to Fig. 4 but showing an alternate method of construction for the locking members which are here shown in the unlocked position.

Referring to the drawings, there is shown in Fig. 5 a fragmentary portion of a firearm embodying the breech locking mechanism of this invention. A hollow cylindrical bolt locking sleeve 5 is fixedly secured in any suitable manner to some immovable portion (not shown) of the firearm. A conventional barrel 1 is removably secured to sleeve 5 by a pair of oppositely disposed bayonet lugs 6 (Figs. 1-2). Barrel 1 is, of course, provided with a chamber 8 into which cartridges 9 are arranged to be fed by means of suitable mechanism (not shown). A breech lock actuator Il! is slidably mounted in the firearm and is provided with an arch-like front portion I I arranged to fit about the top half of sleeve 5. Extending rearwardly from portion I I is a pair of rectangular arms I2 each arranged to slidably fit in a rectangular slot I3 provided on either side of sleeve 5. An actuating slide I4 is slidably retained within the firearm and is provided with a stepped shoulder portion I5 as shown in Fig. 5 for contact with actuator Il).

The rear end portion of hollow sleeve 5 is provided with an axial rectangular opening I6. A reciprocating bolt I8 is provided with a front end portion I1, hereinafter referred to as a bolt head and such bolt head is shaped to slidably enter into opening I6 of sleeve 5. A longitudinal hole I9 extends through bolt head I1 and serves as a tunnel for a firing pin 20. Hole I9 is axially aligned with a longitudinal rectangular channel 2| arranged to sldably receive the rectangular rear end 22 of firing pin 25. The sides of channel 2I are cut away as shown at 23 in Fig. 6 to form a pair of upstanding substantially rectangular lugs 24 which are provided with an arcuate front edge 25. A pin 25 extends transversely through the rear end 22 of firing pin 20 and is arranged to protrude on either side thereof so as to engage with the arcuate front edges 25 of lugs 24.

A longitudinal rib 21 extends along either side of bolt I8 rearwardly of bolt head portion I1. Ribs 21 are arranged to slidably engage in a mating channel 23 formed in a bolt extension member 29. The ends of pin 25 are press-fitted or otherwise suitably fixed within the sides of bolt extension 29. As a result, the recoil movement o'f bolt extension 29 will be correspondingly transmitted to bolt I8 as long as pin 26 is engaged with the arcuate front edges 25 of lugs 24.

Bolt locking sleeve 5 is provided with a second rectangular opening 35 arranged to intersect slots I3 and axial opening I6 at substantially right angles thereto. A vertically disposed semi-cylindrical groove 3| is formed in either side of bolt head I1 and is arranged to align with rectangular opening 30 when bolt i5 reaches its battery position relative to barrel 1.

In order to positively lock bolt I 8 to fixed sleeve 5 prior to the discharge of a cartridge in the firearm, there is provided a locking member 32 having a substantially semi-cylindrical body 33 arranged to mate snugly in the groove 3I on the right hand side of bolt head I1. The groove-engaging portion of body 33 is slabbed as best shown at 34 so that locking member 32 will disengage completely from groove 3I with a minimum amount of travel. Extending outwardly from the top of body 33 is a relatively thin rectangular arm 35 substantially half the width of body 33 itself. Since arm 35 extends across the entire top of body 33, there is thus formed a stepped portion 31 for a purpose to be explained. Substantially midway along the vertical height of body 33 and on the side from which arm 35 extends, there is formed an arcuate cam surface 42. The free end of arm 35 terminates in an angular cam surface 35.

A second locking member 45 is likewise provided to engage in the opposite groove 3I, i. e., the groove formed in the left hand side of bolt I8. Locking member 45 is similar to previously described member 32 in that there is provided a body 46 having a stepped portion 41 at the top thereof, an arcuate cam surface 48 on the side, a flat slabbed surface 49 across the groove-engaging portion, and an arm 55 extending therefrom and terminating in an angular cam surface 5I. However, there exists two differences between locking members 32 and 45, not in construction of their various portions but in the location thereof. While body 33 has its arcuate cam surface 42 o-n the side from which arm 35 extends, arcuate cam surface 48 is located on the side of body 46 which has the stepped portion 41. In addition, the angular cam surface 36 at the end of arm 35 slopes in the opposite direction from angular cam surface 5I of arm 50.

Locking members 32 and 45 are assembled into sleeve 5 from opposite sides of transverse opening 30 whereby bodies 33 and 46 are oppositely disposed with arms 35 and 55 in adjacent relationship, the free end of each arm being supported by the stepped portion of the opposite body. As a result, arcuate cam surfaces 42 and 48 are oppositely aligned and face substantially rearwardly as shown in Fig, 6. At the same time, angular cam surfaces 36 and 5I both face forwardly but due to the fact that arms 35 and 50 lie side by side, cam surface 36 is disposed behind cam surface 5I by an amount substantially equivalent to the width of arm 50.

Arch-like portion I I of breech lock actuator Il] is provided with a pair of angular cam cuts 39 arranged to slope in a direction conversely to angular cam surfaces 36 and 5I on the ends of arms 35 and 50, respectively, and to engage the 'asis-Leva.

latter surfaces simultaneously. In order to achieve such simultaneous contact with cam surfaces 36 and 5| which, as explainedV above, lie in staggered relationship, cam cuts 39 must be correspondingly offset in actuator l0. This is accomplished by the provision of a shelf 40 projeoting rearwardly from arch-like portion on the left side thereof. The left hand cam cut 39 is formed in such shelf and therefore is disposed rearwardly of the right hand cam out by an amount sufficient to insure simultaneous engagement with cam surfaces 36 and 5|1. Locking member bodies 33 and 46 are also each provided with a sloping surface 38and 44, respectively, extending do-wnw-ardly from the top thereof and arranged to provide clearance for the interior curvature of arch-like portion H. A pair of curved cam surfaces 4| is provided in the oppositely disposed portions of actuator arms I2 slightly rearwardly of the arch-like' portion Cam surfaces 4| are shaped tocoact with arenateV cam surfaces 42 and 48 in locking member bodies 33 and 46, respectively.

As shown in Fig. 10, locking member 45 may be alternately constructed to include the second arm 50Y extending from the bottomof body 46 and parallel to the upper arm so as to form -a pair of identical arms 50. In such event, locking member 32 would be similarly provided with a pair of arms 35. The provision of a second arm foreach locking member 32 and 45 would, of course, provide a relatively stronger construction should the single arm type of locking member prove too weak for the purpose required.

The battery position of the recoiling parts at the moment of firing isv illustrated in Fig. 2. When cartridge 9 is fired, the gases evolved cause actuating slide i4 to recoil in a manner conventional to firearm art. The recoiling movement of slide I4 is in turn transmitted to actuator |9- which contacts bolt extensionv 29 and consequently all three parts recoil together. As actuatoi` I0 moves rearwardly, angular cam cuts 39 simultaneously contact the conversely sloped cam surfaces 35 and 5| at the ends of locking member arms 35 and 50, respectively, and force lockingbodies 33 and 45 out of the semi-cylindrical grooves' 3| `in bolt head As soon asl bolt- |8 is completely unlocked and free to move rearwardly, pin 26,. which heretofore has-been moved along the cutaway portion 23 of bolt |13y and has withdrawn firing pin 29 to its pre-fired position, comes in contact with the arcuate front edges 25 of lugs 24. At this time, the recoiling movement of actuator I9 is stopped by contact of breech lock arch-like portion with some fixed part (not shown) in the firearm. However, bolt extension 29 continues to recoil and carry with it the bolt i8 by means of pin 26 thereby effecting extraction of the red round from barrel chamber 8. During. this portion of recoil movement, suitable latch means (not shown) in extension 2.9 engages bolt i8 so that when the former is finally halted by a conventional buffer mecha.- nism (also not shown), the recoil movement. of bolt i8 is effectively halted as well. Counterrecoil of the moving parts of the firearm is now ready to take place.

Since bolt I8 and bolt extension 29 are latched together as mentioned above, they move forwardly simultaneously until a forwardly facing shoulder 43 at the bottom of bolt I8 contacts the front face of bolt locking sleeve 5. At this point bolt I8 and bolt extension 29 have become unlatched and furthermore bolt I8 is now fully home with semi-cylindrical grooves 3| 1n alignment with locking bodies 33 and 46. Just prior to the occurrence of the unlatching action, bolt extension 29 has contacted the ends of breech lock actuator arms |2v and consequently counter recoil movement is transmitted thereto. Thus, as bolt extension 29 and breech lock actuator i3 move forwardly, the curved cam surfaces 4| of the latter act upon the arcuate cam surfaces 42 and 48. of locking members 32 and 45 to' cam locking bodies 33l and 46 into engagement with the. semi-cylindrical grooves 3| on either side of bolt head Il. Bolt extension 29 and breech lock` actuator ||ll continue to move forwardly until the latter is stopped by contacting shoulder I5 in actuating slide I4. During this period of counter-recoil, pin 26 which is fixedly secured to bolt extension 29 moves out of engagement with lugs 24 and rides along` cutaway portion 23 in bolt I8 thereby carrying firing pin 2|) forwardly to fire a cartridge 9 and initiate the recoil cycle previously described.

It will be noted, as shown in Fig. 3, that the configuration of locking bodies 33 and 46 assures a full mating contact with each semi-cylindrical groove 3|. This close t will be maintained regardless of any variation in the depth of engagement between locking members 32 and 45 andbolt i8 due to a possible uctuation in tolerances or the occurrence of wear in the locking surfaces. Thus, once bolt I8 is locked in battery position, any movement along its longitudinal axis which could affect headspace is substantially eliminated. Accordingly, it is readily apparent that the breech locking. mechanism of this invention produces a locking engagement between the reciprocable bolt and a fixed member of the firearm which is far superior` to the tangential point of contact existing in the prior art type of breech lock previously described.

Another advantageous feature provided by the breech lock mechanism of this invention is the simplicity of providing locking grooves in the bolt itself rather than in the fixed member of the firearm as in the prior art type of mechanism. The locking recesses need only be of sufficient depth to assure full contact with the semicylindricalv surfaces of the locking members in contrast to the full transverse hole carried by the prior art type of bolt. Simplicity of manufacture is, of course, a vital factor in reducing the cost of production. Furthermore, since comparatively little stock is removed from the bolt in order to form grooves 3|, there is here provided a comparatively stronger bolt than would be required with the prior art type of breech lock mechanism. y

Referring again to Fig. 3 of the drawings, it will be noted that the sides of locking bodies 33 and 46 are arranged to fit snugly into semicylindrical grooves 3l in bolt head I'I as well as against the sides of sleeve 5 formed by opening 30. It can thus be readily seen that the recoil thrust of locking members 32 and 45 is distributed over a much greater area of bolt sleeve 5 than in the prior type wherein the surface of the roller member is tangent to the relatively sharp rim produced by the transverse hole in the bolt. Excessive wear and deformation of the locking members are consequently kept to a minimum by the larger area of surface contact provided when the locking members of this invention are in a bolt locking position.

I claim:

1. )In a firearm having a barrel, a reciprocable bolt,V and a firing pin slidably mounted in the bolt, the combination of, a tubular member fixedly secured Within the firearm and having one end arranged to slidably receive the frontend of the bolt, means at the opposite end of said tubular member for detachably retaining the breech end of the barrel, a bolt extension having a channel for slidably receiving the rear end of the bolt, means for fixedly securing the firing pin to said bolt extension, an actuator member slidably engaged with the exterior of said fixed tubular member and arranged to transfer recoil movement thereof to said bolt extension, lug means on the bolt for engagement with said ring pin securing means whereby rearward movement of said bolt extension retracts the bolt and firing pin, a pair of locking members slidably retained in said tubular member and arranged for movement transverse of the longitudinal axis of the bolt, a first means in said actuating member for carnming Vsaid locking members outwardly to unlock the bolt from said fixed tubular member, and a second means in said actuator member for camming said locking members inwardly to engage with and lock the bolt to said tubular member in a battery position.

2. In a firearm having a fixed barrel and a reciprocable bolt, the combination of, a tubular member fixedly secured within the firearm, means at the front end portion of said tubular member for releasably retaining the barrel thereto, the rear end portion of said tubular member arranged to receive the front end portion of the bolt, a reciprocating actuator member slidably engaged with the exterior of said tubular member, said tubular member having an opening therethrough disposed at right angles to the longitudinal axis thereof, a pair of locking members slidably retained in said rectangular opening and arranged to engage with the bolt, each of said locking members having a body portion and an arm extending therefrom, each of said body portions having an arcuate surface thereon, said arms having an angular cut at the free end thereof, first cam means in said actuator member arranged to contact said angular cuts at the free end of said arms of said locking members whereby recoil movement of said actuator member actuates said locking members outwardly to disengage from the bolt, and second cam means in said actuator member arranged to contact said arcuate surfaces on said body portions whereby counter-recoil movement of said actuator member returns said locking members into locking engagement with the bolt.

3. Means for locking and unlocking a longitudinally reciprocating bolt in a rearm comprising, a tubular member fixedly secured in the rearm, said tubular member having a substantially rectangular opening therethrough disposed transversely of the longitudinal axis thereof, the bolt having a semi-cylindrical vertical recess on either side thereof arranged to be aligned with said rectangular opening in said tubular member when the bolt reaches battery position, a pair of locking members each having a substantially semicylindrical body' arranged to fit snugly within said recesses in the bolt, a relatively narrow arm portion extending outwardly from the top of each of said bodies, a downwardly stepped portion on the top of each of said bodies adjacent said arm portions, said locking members arranged to be inserted into opposite ends of said rectangular opening in said tubular member with the arm of one member slidably supported on the stepped portion of the other member whereby said bodies are oppositely disposed and aligned with said recesses in the bolt when the latter is in battery position, first cam means for simultaneously actuating said locking members transversely of the longitudinal axis of the bolt into locking engagement with said recesses in the bolt, and second cam means for simultaneously actuating said locking members out of engagement with the bolt.

4. The construction of claim 3 wherein said locking members are each provided with a pair of parallel arms disposed at the top and bottom or' said bodies and extending outwardly in the same direction, and said bodies are each provided with a stepped portion on the top and bottom thereof for slidably supporting the free ends of said arms.

5. In a firearm having a barrel, the combination of, a tubular member fixedly mounted in the firearm, means in said fixed tubular member for releasably securing therein the breech end of the barrel, a longitudinally reciprocable bolt having a substantially rectangular bolt head, said bolt head having a semi-cylindrical groove on either side thereof, said xed tubular member having a rear end rportion arranged to slidably receive said bolt head into battery relationship with the barrel, said tubular member havingV a pair of oppositely disposed longitudinal slots extending forwardly from the rear end thereof, said tubular member alsohaving a substantially rectangular opening arranged to extend transversely therethrough and intersect said slots, a pair of locking members having a body portion and an arm extending outwardly from the top thereof, said body portion arranged to slidably nt into said transverse opening and engage into said grooves in said bolt head, said arm of one locking member extending toward said body portion of the other locking member and lying in adjacent relationship, a reciprocable actuator having an arch-like body portion and a pair of legs extending rearwardly therefrom, said arch-like portion arranged to t about the top half of said tubular member with said legs slidably engaged in said slots thereof, nrst cam means in said actuator for camming said locking members outwardh7 to disengage from said bolt head upon the recoil stroke of said actuator, and second cam means in said actuator for camming said locking members inwardly to reingage with said grooves in said bolt head upon the counter-recoil stroke of said actuator.

6. In a firearm, a breech locking mechanism comprising, a tubular member fixedly secured in the iirearm, a longitudinally reciprocating bolt having an integral head portion arranged to extend into said fixed tubular member when in a battery position, said bolt head portion having a semi-cylindrical vertically disposed groove on either side thereof, said tubular member having a transverse opening therethrough arranged to align with said grooves when said bolt is in its battery position, a pair of locking members each arranged to slidably fit into one end of said transverse opening in said tubular member, said locking members having a body and an arm extending outwardly from the top thereof, said bodies having a stepped portion on the top thereof, located so as to support the end of said arm of the opposite one of said locking members, said bodies having a substantially arcuate portion arranged to engage snugly into said grooves of said bolt and having nat por tions on either side thereof rearwardly ofsaid arcuate portions for slidable engagement With the walls of said transverse opening in said tubuiar member, an arcuate cam surface on each of said bodies located substantially midway along the vertical axis thereof'and arranged to face rearwardly when said locking members are assembled, an angular cam surface at the free end of each of said arms arranged to face forwardly when said locking members are assembled, and reciprocable means for engaging said angular cam surfaces on said arms to cam said locking members out of engagement with said bolt during recoil and for engaging said arcuate cam surfaces on said locking bodies to cam said locking members into engagement with said bolt during counter-recoil.

7. In a firearm, a breech locking mechanism comprising, a tubular member xedly secured in the firearm, a longitudinally reciprocating bolt, an integral head portion arranged to extend into said fixed tubular member when in a battery position, said tubular member having a transverse opening therethrough, a pair of locking members arranged to slidably t into one end of said transverse opening, said locking members having a body and an arm extending outwardly from the top thereof, an angular cam surface at the free end of each of said arms, said arms arranged to lie side by side in said tubular member whereby said angular cam surface on one of said arms is disposed forwardly of the other, a reciprccable actuator member having an archlike portion, a pair of angular cam cuts in said arch-like portion, and a rearwardly extending shelf disposed on one side of said arch-like portion and arranged to contain the angular cam out in such side whereby one of said cam cuts is located rearwardly of the other, al1 arranged 10 and adapted whereby said angular cam cuts in said actuator member simultaneously contact said angular cam surfaces at the free ends of said arms to cam said locking members out of engagement with said bolt during recoil.

8. In a firearm, a breech locking mechanism comprising, a tubular member xedly secured in the firearm, a longitudinally reciprocating bolt arranged to extend into said fixed tubular member when in a battery position, a pair of oppositely disposed locking members slidably retained in said fixed tubular member for movement in a direction transverse of the longitudinal axis of the bolt, said tubular member having a slot on either side extending forwardly from the rear face thereof, a reciprocable actuator having an arch-like body portion and a pair of legs extending rearwardly therefrom, said actuator arranged to slidably engage said tubular member with said arch-like portion surrounding the outer periphery of the former and with the inner sides of said legs in said slots, said arch-like portion having a pair of angular cam cuts therein for camming said locking members out of engagement with said bolt whereby the latter is free to recoil, and each of said legs having an arcuate cam surface in opposed relationship for camming said locking members into engagement with said bolt whereby the latter is locked to said tubular member.

CLARENCE E. SIMPSON.

References Cited in the le of this patent FOREIGN PATENTS Numlber Country Date 256,030 Italy Dec. 3, 1937 263,143 Italy Mar. 7, 1939 483,319 Germany Sept. 30, 1939 (Duplicate of Italy) 

